The invention relates to a seat belt force limiter and a method for restraining an occupant of a vehicle.
In particular, and not exclusively, the present invention relates to the reduction of the danger of injury to vehicle occupant by means of a restraining system having a crash sensor, a three-point safety seat belt and an apparatus for limiting the seat belt force.
In the state of the art it is known to protect vehicle occupant in case of an accident by means of a three-point safety belt; when the crash sensor is triggered, first a belt tensioner is activated, and after the belt is tightened and the belt spool is clutched, a device for energy absorption is activated which limits the belt forces acting on the vehicle's occupant.
Belt force limiters are known in which the belt force limitation is achieved in principle by the rotation of a torsion bar. Such belt force limiters generally have a flange, a spool for winding and unwinding the belt, and a torsion bar. In case of an accident the flange is antitorsibly locked and connected by means of a locking device to the vehicle's structure, while the belt wound on the spool can unwind with a limited force resulting from the torque of the torsion bar.
Also, two-stage belt force limiters have been proposed wherein the belt force level is reduced in a second, additional stage. Embodiments heretofore, however, are very complicated and too expensive.